This invention is generally directed to toner and developer compositions, and more specifically, the present invention is directed to processes for deinking, or removing toner from paper, a transparency, and the like. In embodiments, the present invention relates to the deinking of substrates fused with toner, such as paper, transparencies, and the like, containing an image developed with a toner comprised of an imide or amic acid based resin and pigment. The process of the present invention, in embodiments, involves the contacting or soaking of the fused image, such as a xerographic image, in an aqueous solution comprised of a mixture of certain ionic salts such as a mixture of sodium chloride, sodium phosphite, ethylenediaminetetracetic acid, tetrasodium salt and the like, and surfactants, preferably a nonionic surfactant such as TRITTON X-100.RTM., and wherein the pH of the solution is basic, for example in excess of about 7, and preferably 8 or more, and which pH can be attained with the addition of caustic reagents such as sodium bicarbonate, sodium hydroxide and the like, and thereafter dissolving the toner resin and removing the liberated dispersed pigment from the substrate by filtration or flotation and washing. The dissolved toner resin can then be optionally reclaimed from the washed aqueous phase by adjusting the pH to 7 or less, which adjustment can be accomplished by the addition of a dilute acid resulting in the precipitation of the imide or amic acid based resin, and thereafter filtered off. Preferably, the toner compositions deinked are comprised of imide based resins such as polyimides, and polyester imides, amic acid based resins such as a polyamic acid, polyester amic acid, or mixtures thereof, and pigment particles comprised of, for example, carbon black, magnetites, or mixtures thereof, cyan, magenta, yellow, blue, green, red, or brown components, or mixtures thereof.
Paper recycling has become an important environmental issue in recent years, and deinking of conventional dry toner images can be a much more difficult problem for the paper recycling industry than that of conventional impact printing inks. The recycling industry utilizes various deinking processes, and the first step is usually to repulp the waste paper in an agitated caustic bath. More specifically, the process involves shredding the paper in an agitated aqueous slurry of about 10 percent consistency by weight of paper at a pH of about 10 to about 11.5. The aforementioned pH is attained by the addition of caustic soda or sodium bicarbonate. The aqueous slurry is then heated at an ambient temperature to about 60.degree. C. for a duration of from about 30 minutes to about 200 minutes. During this repulping stage, the paper absorbs large amounts of water, swells considerably, and is reduced to a slurry of individual hydrated pulp fibers, and various inks are detached from the fibers by differential swelling or disintegration. Dry toner images do not usually swell because of their hydrophobic polymeric composition, and they are not usually degraded by chemical hydrolysis. Dry toner images result in flat platelets about 100 to 200 microns in average diameter and about 10 microns in thickness as measured by microscopic image analysis methods. Conventional impact printing inks are found to disintegrate into much smaller particles, typically 10 microns or less in diameter, primarily because they contain no fused thermoplastic binder resins.
Subsequent steps in the deinking process are designed to remove the liberated ink specks from the hydrated pulp slurry. With small specks liberated from impact-printed papers, these steps are simple and efficient. One or two washing cycles are often sufficient to rinse the small liberated ink specks from the slurry to adequate cleanliness. If this is insufficient, a flotation cell can be added to further clean the pulp. When the waste paper is imaged with dry toner, the slurry contains the much larger aforementioned toner platelets. To achieve adequate cleaning of such pulps, the recycling industry has found it necessary to employ a much more elaborate process. Typically, this comprises six flotation cells in series. Subsequently, the pulp is dewatered in preparation for a high-shear dispersion step to further break up the remaining specks. The dispersion step is energy intensive, and is accompanied by a certain amount of fiber damage. Following this and a redilution step, up to another four flotation steps may be required to remove the broken specks to an adequate cleanliness.
In the present invention, a process for the deinking of toner compositions comprised of an imide or amic acid based resin with pigment is illustrated. More specifically, this process is comprised of dissolving the imide or amic based toner resin in aqueous media under milder caustic repulping conditions of a pH of about 8 to about 10 in the presence of ionic salts, such as sodium chloride, sodium phosphite, ethylene diamine tetracetic acid tetrasodium salt, and optionally a nonionic surfactant, such as TRITTON X-100.RTM., NEOGEN.RTM., or NEOGEN SC.RTM. and the like, at from about ambient temperature to about 80.degree. C. These conditions cause the imide or amic acid based toner resin to dissolve in the aqueous phase and liberate pigment particles to less than or equal to about 0.5 micron, and preferably from about 0.05 micron to about 0.255 micron in average volume diameter. This enables the use of the aforementioned simple ink speck removal typically effective only for impact-printed papers. Therefore, the toner ink specks are much easier to remove resulting in a more economical process and superior quality pulp. This differs from the conventional deinking process wherein the toner resin particles are not dissolved but broken down in particle size by the mechanical action, and require more aforementioned elaborate flotation and washing techniques to remove the toner particle specks from the pulp slurry.
The aforementioned imide based toner compositions are illustrated in U.S. Pat. No. 5,348,830, the disclosure of which is totally incorporated herein by reference, and these resins can be generated by a preparative process involving the melt polycondensation of about 1 mole equivalent of dianhydride, and from about 1 mole equivalent of an alkylene diamine, or preferably a diamino terminated alkylene oxide, such as the diamino terminated polyalkylene oxide available from Texaco Chemicals as JEFFAMINE D-230.TM., D-400.TM., D-700.TM., EDR-148.TM., EDR-192.TM. as illustrated by the formulas ##STR1## wherein
______________________________________ EDR-148 .TM. n = 2; R = H EDR-192 .TM. n = 3; R = H D-230 .TM. n = 2,3; R = CH.sub.3 D-400 .TM. n = 5,6; R = CH.sub.3. ______________________________________
The aforementioned resins exhibit a number average molecular weight of from about 1,500 to about 50,000 grams per mole as measured by vapor phase osmometry, and a glass transition temperature of from about 40.degree. C. to about 80.degree. C., and more preferably of from about 50.degree. C. to about 65.degree. C. as measured by the Differential Scanning Calorimeter.
There is disclosed in U.S. Pat. No. 5,411,831 toner compositions comprised of a crosslinked polyimide resin and pigment, and process thereof. There is also disclosed in U.S. Pat. No. 5,413,888 gloss switching toners with certain polyimides. The toner compositions of the U.S. Pat. No. 5,411,831 are crosslinked to about 30 gel or more and are believed to yield with broad fusing latitude characteristics, and moreover result in low gloss characteristics and not high gloss.
Illustrated in the following U.S. Patents, the disclosures of each being totally incorporated herein by reference, are:
U.S. Pat. No. 5,348,831, which illustrates a toner composition comprised of pigment, and a polyester imide resin of the formula ##STR2## wherein n represents the number of segments present and is a number of from about 10 to about 10,000; R' is alkylene; and R is independently selected from the group consisting of an oxyalkylene and polyoxyalkylene.
Illustrated in U.S. Pat. No. 5,552,254, the disclosure of which is totally incorporated herein by reference, are toners containing polyamic acid resins of the formulas ##STR3## wherein X is a tetrasubstituted aromatic or cycloaliphatic group with from about 6 to about carbon atoms, R is alkylene, alkyleneoxyalkylene or poly(alkyleneoxy)alkylene; and R' is a divalent aromatic, cycloaliphatic or aliphatic group, and n and m represent random segments of the polymer. In embodiments, the aforementioned polyamic based toners can be deinked using the conditions of this invention, and more specifically, at a pH of about 8.0 with certain ionic salts and optionally a nonionic surfactant. Similarly, there is further illustrated in U.S. Pat. No. 5,512,401, the disclosure of which is totally incorporated herein by reference, toners containing polyimide amic acid resins.
Illustrated in U.S. Pat. No. 5,409,293, the disclosure of which is totally incorporated herein by reference, are deinkable toners containing polyimide-imine, polyimides, and wherein the deinking involves resin decomposition in alkaline or caustic aqueous conditions at a pH of from about 10 to a pH of about 14.
Illustrated in U.S. Pat. No. 5,411,829, the disclosure of which is totally incorporated herein by reference, are deinkable toners containing a cycloaliphatic polyimide resin, and wherein the deinking involves resin dissolution in alkaline or caustic aqueous conditions at a pH of from about 10 to a pH of about 14.